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Nitrogen fixation refers to any natural or industrial process that converts atmospheric nitrogen gas (N2) into more reactive nitrogen compounds like ammonia, nitrates, or nitrites.
- The air in the Earth’s atmosphere consists of 78% Nitrogen gas.
- Nitrogen forms the backbone of many cellular components.
- These include amino acids, the building blocks of proteins, and nucleic acids like DNA and RNA, which carry the genetic code of life.
- Despite its large availability, the usable form of nitrogen is very low.
- The process of nitrogen fixation converts nitrogen molecules into a usable form.
- The conversion occurs through various biological and natural processes.
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Key Terms: Nitrogen, Bacteria, Rhizobium, Azotobacter, Ammonia, Lightning, Nitrogen-fixing bacteria, Prokaryotes, Enzymes
What is Nitrogen Fixation?
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Nitrogen fixation is the process of converting molecular N2 gas into a reactive, biologically available form of nitrogen.
- It is the first stage of the nitrogen cycle.
- During nitrogen fixation, atmospheric nitrogen is converted into usable forms, such as ammonia.
- This can be done by specific bacteria like Rhizobium and Azotobacter as well as through other natural phenomena.
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Type of the Nitrogen Fixation
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Plants are the primary source of food for many organisms, but they cannot directly utilize atmospheric nitrogen for protein synthesis. Unlike carbon dioxide and oxygen, which they absorb through their stomata (leaf pores), plants rely on nitrogen from the soil.
- Nitrogen gas in the environment cannot be directly used by plants.
- There are various bacteria and natural phenomena that help in nitrogen fixation.
Different types of Nitrogen Fixation are
- Biological Nitrogen Fixation
- Natural Nitrogen Fixation
Biological Nitrogen Fixation
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Biological nitrogen fixation refers to the conversion of atmospheric nitrogen into ammonia through certain bacteria and prokaryotes.
- The enzyme nitrogenase converts dinitrogen into ammonia.
- Nitrogen-fixing bacteria can be free-living or symbiotic.
- Some free-living nitrogen fixers include Azotobacter, Beijernickia, Rhodospirillum, and cyanobacteria.
- Symbiotic nitrogen fixers include Rhizobium (in legume root nodules) and Frankia (in non-leguminous plant root nodules).
Symbiotic Nitrogen Fixation
A specific species of bacteria, called Rhizobium plays an important role in nitrogen fixation.
- These bacteria reside in the roots of leguminous plants (e.g., peas and beans).
- Using specific enzymes, these bacteria help nitrogen fixation within the soil.
- During this symbiotic process, they convert the unusable form of atmospheric nitrogen into a usable form, such as ammonia (NH3).
- This converted nitrogen dissolves in the soil, allowing plants to readily absorb it.
- This is why farmers use crop rotation, in which leguminous plants help restore nitrogen levels in the soil without the need for fertilizers.
Natural Nitrogen Fixation
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This type of nitrogen fixation refers to natural processes other than biological nitrogen fixation such as Nitrogen fixation by lightning.
Nitrogen Fixation by Lightning
Lightning strikes create high temperatures and pressures that break the N2 bond, allowing nitrogen to react with oxygen to form usable forms like nitrates and nitrites.
- The contribution of lightning in nitrogen fixation is much less.
- Despite its smaller contribution, it helps prevent nitrogen deficiencies in plants.
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Things to Remember
- Nitrogen fixation is the phenomenon that converts atmospheric nitrogen gas (N2) into more reactive nitrogen compounds.
- Biological nitrogen fixation is the conversion of atmospheric nitrogen into ammonia through certain bacteria and prokaryotes.
- Symbiotic nitrogen fixers include Rhizobium and Frankia.
- The enzyme nitrogenase converts dinitrogen into ammonia.
- Lightning strikes create high temperatures and pressures that break the N2 bond, allowing nitrogen to react with oxygen.
Sample Questions
Ques. What do you mean by nitrogen fixation? (2 Marks)
Ans. It is a natural process of converting molecular nitrogen into its nitrogenous forms using natural or biological methods. This nitrogen is used mostly by a farmer in agriculture.
Ques. What is denitrification? (2 Marks)
Ans. It is the process of converting nitrates back into inert nitrogen gas. This process is done during the absence of oxygen by bacteria species like Clostridium and Pseudomonas.
Ques. Why is nitrogen fixation important for the earth? (2 Marks)
Ans. Nitrogen fixation is important for Earth because it provides a vital form of nitrogen that living organisms require to synthesize the basic building blocks of plants, animals, and many other organisms.
Ques. What are the different types of nitrogen fixation? (2 Marks)
Ans. The different types of nitrogen fixation are
- Nitrogen fixation in nature
- Industrial nitrogen fixation
- Lightning Nitrogen fixation
- Symbolic Nitrogen Fixation
Ques. What is the factor affecting nitrogen fixation? (1 Mark)
Ans. The factors affecting nitrogen fixation are pH, salinity, moisture, temperature, microorganisms, organic matter, and soil texture.
Ques. What is the main thing responsible for nitrogen fixation? (1 Mark)
Ans. The nitrogen-fixing bacteria are more than 90% responsible for nitrogen fixation and they play an important role in this.
Ques. What condition is needed for nitrogen fixation? (1 Mark)
Ans. The Haber process needs high pressure (around 200 atm) and high temperature (around 400 cells) required for industrial nitrogen fixation.
Ques. What are the important enzymes involved in nitrogen fixation? (1 Mark)
Ans. The enzymes called the nitrogenous need for nitrogen fixation.
Ques. Write about the process of nitrogen fixation in nature. (3 Marks)
Ans. The nitrogen is combined with nature as the nitric oxide by lightning and ultraviolet rays but a large amount of nitrogen is fixed as ammonia, and nitrates by soil microorganisms. More than 90% of all nitrogen fixation is affected by them. These are organisms that utilized the enzyme nitrogenase for the catalyzed conversion of nitrogen (N2) to ammonia (NH3). Plants readily assimilate NH2 to produce the aforementioned nitrogenous.
Ques. How is nitrogen returned to the atmosphere? (2 Marks)
Ans. Nitrogen is the return to the atmosphere by an organism called a decomposer. Some bacteria are decomposers and break down the complex nitrogen compounds in dead organisms and animal wastes.
Ques. What is meant by symbiotic nitrogen fixation? (3 Marks)
Ans. A special type of bacteria called Rhizobium helps in nitrogen fixation. These bacteria are present in the root of the plant and use a certain type of enzyme, which helps in fixing nitrogen in the soil. In all these processes they convert non-absorbable nitrogen form into a usable form. It easily dissolves in the soil and plants absorb modified nitrogen from soils. It is one of the major sources of nitrogen for crop production, and it is estimated that Nitrogen fixed by the genus Rhizobium ranges between 200 to 500 kg ha-1 in the case of many leguminous plants. It is done by rhizobia in root nodules of crop and forage legumes giving a substantial economy and environmental protection.
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